Various types of stereoscopic projection optical systems are well known in the art. Such stereoscopic projection optical system includes two projectors arranged in parallel so that image from a liquid crystal display (LCD) panel or a slide film is projected on a screen by each light source. As shown in FIG. 4, one of such stereoscopic projection optical systems includes spherical reflective mirrors 1, 1′, lamps 2, 2′, condenser members 3, 3′, LCD panels 4, 4′, and projecting lenses 5, 5′.
In the stereoscopic projection optical system of FIG. 4, the stereoscopic picture is obtained by making the polarizing directions of projected beams perpendicular to each other by using two projectors, and then the picture from a right projector is visible only to right eye of a viewer and the picture from a left projector is visible only to left eye of the viewer, respectively.
In the conventional projection optical system, the lamps 2, 2′ are independently operated and when the beams from the lamps 2, 2′ pass through the LCD panels 4, 4′, the beams are polarized in the direction of a polarizing axis of polarizing plates of the LCD panels 4, 4′. At this time, a half of the beams condensed by the condenser members 3, 3′ is decreased before having passed through the LCD panels 4, 4′ by one polarizing plate which is located at the light source side. A loss of light occurs due to a part of light being absorbed as a heat to the polarizing plate of the LCD panels 4, 4′, thereby necessitating a separate cooling device to increase the cooling efficiency at the LCD panels 4, 4′.
It is desired to provide a stereo projection optical system which can overcome the above-described deficiencies.